The present invention relates to an apparatus for ventilating the crankcase of a combustion engine, comprising a ventilation duct running from the crankcase to an intake section of the combustion engine and at least one oil-mist separator that causes a pressure drop and is arranged in the course of the ventilation duct, with a crankcase vacuum pressure regulating valve that is installed upstream or downstream of the oil-mist separator and is adjustable dependent on the crankcase pressure such that the pressure in the crankcase is prevented from falling below a lower pressure limit value.
During operation of a combustion engine, gas is pressed out of the combustion chamber and into the crankcase through the gap between the piston rings and the cylinder walls, this gas being called blow-by gas. This gas increases the pressure in the crankcase and must, therefore, be removed. Usually, the blow-by gas is supplied into the intake section of the combustion engine via a crankcase vacuum pressure regulating valve. Emission of noxious substances out of the crankcase is, thus, avoided. The regulating valve is provided to maintain a range of pressure in the crankcase that is optimal from a technical point of view. Too low a crankcase pressure must be avoided in order to prevent foreign substances from entering into the crankcase from outside through leaks. Too high a crankcase pressure must, vice versa, also be avoided in order to prevent oil or gas from exiting through leaks in an uncontrolled manner.
The blow-by gas contains fine oil particles in the form of oil mist which might cause malfunctions of the combustion engine when the gas is being returned into the intake section of the combustion engine. For that reason, the oil mist must be separated from the gas. To achieve this, at least one separator is arranged in the course of the ventilation duct carrying the blow-by gases, usually either as a coalescer made of textile fiber materials or as a cyclone. An apparatus for ventilating the crankcase of a combustion engine comprising the features and functions illustrated above is described in the applicant's non-prepublished German utility model registration application 200 09 605.2.
The performance of the separator in such an apparatus is, in particular, determined by the flow resistance that is generated by the respective blow-by gas volume flow. In this context, it can generally be observed that a high separation rate is associated with a high flow resistance and vice versa. The flow resistance in the separator is a disadvantage in that it also increases the pressure in the crankcase accordingly. If the combustion engine is, for example, in operating states where it is subject to high speeds and high load, this increase in pressure in the crankcase is compensated by the high vacuum pressure that is then present in the intake section. In this manner, the pressure in the crankcase is prevented from assuming too high values. If, however, the vacuum pressure in the intake section of the combustion engine is only low, as is the case at low speeds or in the deceleration mode of the combustion engine, then there is the risk of the pressure in the crankcase rising to an impermissibly high value.